Michael Higdon surpassed Willie Pettigrew's post-war goalscoring record for Motherwell with a stunning double that gives Celtic the chance to win the title themselves.
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Celtic would have been crowned Clydesdale Bank Premier League champions if Motherwell had failed to win but that scenario never looked likely from the second minute when Higdon fired the first of two accurate long-range strikes.
Henrik Ojamaa soon added another and Higdon took his tally for the season to 24 SPL goals - and 25 in total - before Jon Daly pulled one back.
In doing so, the Englishman beat Pettigrew's record for the most top-flight league goals for Motherwell in a season since the Second World War.
Higdon's accolade, which beat Pettigrew's personal best from 1975-76, is all the more impressive considering the likes of Ian St John, Joe McBride, Brian McClair and Tommy Coyne have graced the claret and amber jersey before him.
Celtic will now get the title party opportunity they might have been denied by the controversial post-split fixture scheduling, which sees Neil Lennon's men host Inverness on Sunday needing a point to retain the championship.
While the victory had important ramifications for Celtic, it also takes Motherwell a huge step towards sealing the top-three place that would seal their fifth season in Europe in six years.
Stuart McCall's side are now six points clear in second place and 11 ahead of fourth-placed St Johnstone.
Higdon has scored a variety of goals this season but arguably none as good as the opener, which had a sublime supporting role from James McFadden, who made space for himself with a drag-back that took out several opponents before slipping the ball inside to the former St Mirren striker.
The ball bobbled slightly but Higdon cut across it perfectly to send a swerving effort in off the top of the post.
Ryan Gauld shot just over after a one-two with John Rankin on the edge of the box at the other end but the opening stages were otherwise a Motherwell onslaught with McFadden running amok with some superb pieces of skill.
Chris Humphrey forced a good save from Radoslaw Cierzniak before Ojamaa netted his first goal of 2013 and only his third of the season, although the striker tops the SPL assists chart.
The eighth-minute goal saw a role reversal with Higdon guiding a lay-off into the path of the onrushing Estonian, who knocked the ball past a defender before stabbing it past Cierzniak.
McFadden was tormenting United right-back Brian McLean and he fired wide after a typical charge to the edge of the box.
Motherwell could have made a lot more of several other openings before taking their foot off the gas, and Darren Randolph made some important first-half saves, the first from Jon Daly at his near post following a cutback from Stuart Armstrong.
The Irishman was then alert to deny Gauld before pulling off an impressive diving save to stop the second of two quickfire efforts from Gary Mackay-Steven.
Motherwell rediscovered their attacking intent after the interval and Ojamaa came close with an ambitious effort before Higdon made it three.
The Liverpudlian took the ball in from Humphrey 20 yards out, held off and turned John Souttar before drilling the ball inside the far corner.
United had only previously lost to Celtic - in the league and last weekend's William Hill Scottish Cup semi-final - since Jackie McNamara took over in January and they showed enough spirit to prevent the game drifting towards the end.
Willo Flood came close with a free-kick before Daly guided the ball through the legs of Randolph in the 69th minute after Mackay-Steven had forced the ball into his path.
Randolph soon pushed Mackay-Steven's drive wide but Motherwell repelled the pressure and should have added to their lead with a four-against-two counter-attack only for both Humphrey and Ojamaa to take the wrong option.